1. Field of the Invention
The present invention relates to a method and a machine for grinding cylindrical surfaces of workpieces with a circular grinding wheel.
2. Description of the Prior Art
A conventional angular grinding wheel is shown in FIG. 1, where a workpiece W has a cylindrical surface and a shoulder portion to be ground. The grinding wheel has a cylinder-grinding surface 1 and a shoulder-grinding surface 2 perpendicular to the cylinder-grinding surface 1 whose generatrix is parallel to the generatrix of the cylindrical surface to be ground. The shoulder-grinding surface 2 grinds the shoulder portion of the workpiece. Where the cylindrical surface is ground with this angular grinding wheel, the wheel is moved toward the central line of the workpiece W in a direction intersecting the cylindrical surface so that the wheel may be fed into the workpiece. Then, the wheel is moved relative to the workpiece along the generatrix of the cylindrical surface. As a result, the cylindrical surface of the workpiece W is machined with the cylinder-grinding surface 1 of the angular grinding wheel by traverse grinding.
Since the cylinder-grinding surface 1 of this grinding wheel is completely parallel to the generatrix of the ground cylindrical surface, the front edge E of the grinding surface 1 as viewed in the direction of movement as shown in FIG. 1 is worn too quickly.
In the conventional traverse grinding, it is difficult to obtain a desired surface finish and quite accurate dimensional tolerances if the grinding wheel traverses the cylindrical surface of the workpiece only once. Therefore, three machining steps, i.e., rough grinding, accurate grinding, and finishing grinding, are normally needed. Consequently, it is impossible to machine the cylindrical surface in a short time.